The present invention generally relates to the field of chemical mechanical polishing (CMP). In particular, the present invention is directed to a CMP pad having unevenly spaced grooves.
In the fabrication of integrated circuits and other electronic devices on a semiconductor wafer, multiple layers of conducting, semiconducting and dielectric materials are deposited onto and etched from the wafer. Thin layers of these materials may be deposited by a number of deposition techniques. Common deposition techniques in modern wafer processing include physical vapor deposition (PVD) (also known as sputtering), chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD) and electrochemical plating. Common etching techniques include wet and dry isotropic and anisotropic etching, among others.
As layers of materials are sequentially deposited and etched, the surface of the wafer becomes non-planar. Because subsequent semiconductor processing (e.g., photolithography) requires the wafer to have a flat surface, the wafer needs to be periodically planarized. Planarization is useful for removing undesired surface topography as well as surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches and contaminated layers or materials.
Chemical mechanical planarization, or chemical mechanical polishing (CMP), is a common technique used to planarize semiconductor wafers and other workpieces. In conventional CMP using a dual-axis rotary polisher, a wafer carrier, or polishing head, is mounted on a carrier assembly. The polishing head holds the wafer and positions it in contact with a polishing layer of a polishing pad within the polisher. The polishing pad has a diameter greater than twice the diameter of the wafer being planarized. During polishing, the polishing pad and wafer are rotated about their respective concentric centers while the wafer is engaged with the polishing layer. The rotational axis of the wafer is offset relative to the rotational axis of the polishing pad by a distance greater than the radius of the wafer such that the rotation of the pad sweeps out an annular “wafer track” on the polishing layer of the pad. When the only movement of the wafer is rotational, the width of the wafer track is equal to the diameter of the wafer. However, in some dual-axis polishers the wafer is oscillated in a plane perpendicular to its axis of rotation. In this case, the width of the wafer track is wider than the diameter of the wafer by an amount that accounts for the displacement due to the oscillation. The carrier assembly provides a controllable pressure between the wafer and polishing pad. During polishing, a slurry, or other polishing medium, is flowed onto the polishing pad and into the gap between the wafer and polishing layer. The wafer surface is polished and made planar by chemical and mechanical action of the polishing layer and polishing medium on the surface.
The interaction among polishing layers, polishing media and wafer surfaces during CMP is being increasingly studied in an effort to optimize polishing pad designs. Most of the polishing pad developments over the years have been empirical in nature. Much of the design of polishing surfaces, or layers, has focused on providing these layers with various patterns of voids and arrangements of grooves that are claimed to enhance slurry utilization and polishing uniformity. Over the years, quite a few different groove and void patterns and arrangements have been implemented. Prior art groove patterns include radial, concentric circular, Cartesian grid and spiral, among others. Prior art groove configurations include configurations wherein the width and depth of all the grooves are uniform among all grooves and configurations wherein the width or depth of the grooves varies from one groove to another.
More particularly, a number of prior art groove patterns for rotational polishing pads involve grooves that extend from a location near or at the concentric centers of the pads to a location near or at the outer periphery of the pad. Examples of such patterns in the context of radial grooves and spiral grooves appear in U.S. Pat. No. 6,783,436 to Muldowney. All of the radial and spiral groove patterns disclosed in the Muldowney patent have a constant angular pitch in direction around the respective pads, as is typical of such groove patterns. The Muldowney patent also shows polishing pads having Cartesian grid and concentric circle groove patterns. The grooves in both of these patterns have a constant pitch, i.e., the spacing of adjacent grooves is the same. U.S. Pat. No. 5,984,769 to Bennett et al. discloses in one instance a polishing pad having concentric circular grooves arranged such that the pitch of the grooves is changed depending upon where the grooves are located on the pad. In another instance, the Bennett et al. patent discloses a polishing pad in which the pitch between adjacent segments of a single spiral groove varies depending on where the grooves are located on the pad.
While the prior art contains polishing pads having a wide variety of groove patterns, the effectiveness of these grooves patterns varies from one pattern to another, as well as from polishing process to polishing process. Polishing pad designers are continually seeking groove patterns that that make the polishing pads more effective and useful relative to prior art pads.